Well, crap. Is my bike toast?

2008ish Trek 7.3FX, I weigh 110kg(220lb), well within limits. I might have converted it to drops and did about 2000km of loaded touring and maybe 8000km of city riding. Doesn't seem to be an unusual amount of use to me :/ but i got it second hand so no warranty.

it looks like that crack goes all the way around. if so, that chunk of metal above the seat cluster is just for show anyway. so just cut it off and reassemble. or not, it looks like that seat cluster needs a standalone seat clamp and there may not be enough room for it.

this may have been caused by a seat post that was not inserted far enough into the top tube...

too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

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If that's a crack in the seat tube above the Top tube weld,your frame is golden brown, but may not be toast yet.

First of all, understand what is causing it, which is excess stress from an unsupported seat post. The minimum insetion mark on the pot relates to the posts requirements. However, there's a second requirement that the post extend to about 1" below the top tube. On a frame with a design like yours this may mean that the minimum insertionis deeper than the mark indicates.

Also, an undersized post can cause a similar problem by rocking within the tube. If all is right, the post fully supports the seat tube where yours is cracked.

If it isn't cracked all the way around, you might extend the life with a longer, better fitted post, however the crack will probably continue to grow. If you're willing to sacrifice a post to save the frame, and you have no plans to ever adjust the saddle height, you can get a longer seat post and bond it in place with epoxy, or an anaerobic (loctite) adhesive. Once a strong post is bonded in it will hold the frame together through the cracked area.

Given your weight, it may not be a forever repair, but if done right will last a long time.

If you replace the frame, consider a careful fit for the tallest frame you can manage properly. This will shorten the unsupported post reducing stress at the base. Also a frame design with a minimum extension of the seat tube above the joint will prevent this kind of damage.

If you bought the bike new before doing anything crazy go to a trek dealer and try and get them to warranty the frame for you. Trek is usually good about standing behind their products and it is not fair to assume the end user will realize their seatpost is not far enough into the frame if they are not above the min insertion line although what FB say's is spot on. Hopefully they will replace the frame for free and try to find a longer post to offer more support, especially since you need a setback post which would put a little more force on the seat tube.

If you bought the bike new before doing anything crazy go to a trek dealer and try and get them to warranty the frame for you. Trek is usually good about standing behind their products and it is not fair to assume the end user will realize their seatpost is not far enough into the frame if they are not above the min insertion line although what FB say's is spot on. Hopefully they will replace the frame for free and try to find a longer post to offer more support, especially since you need a setback post which would put a little more force on the seat tube.

i agree see your trek dealer.
if you are the original owner it should have a lifetime free replacement warranty.
lots of clydes have broken there frames and gotten free replacements.
someone in the 50+ threads broke his fork steer tube on a 7.6 fx and trek replaced the entire bike.

Looks like a prime candidate for a low temperature Alumi-braze or similar process(like HTS-2000) which can be used with a propane or mapp torch. For that juncture I do not think it would pose any risk if done properly in combination with a longer, tight fitting post.

Call the Trek dealer and see what they can offer, but after riding 10000 km on a used bike, don't get your hopes up. They may offer you a discount on a new bike or frame, but you may be able to get a new or clearourt replacement frame from another manufacturer for cheaper.

England, currently dividing my time between university in Guildford and home just outside Reading

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Originally Posted by mtbikerinpa

Looks like a prime candidate for a low temperature Alumi-braze or similar process(like HTS-2000) which can be used with a propane or mapp torch. For that juncture I do not think it would pose any risk if done properly in combination with a longer, tight fitting post.

How low is "low temperature"? Anything using any kind of flame would have me worried about having to have the heat treatment on the frame redone to avoid weakening the alloy.

I'm using the original bontrager seat post that came with the bike, i'm possitive it's the correct size, 27.2mm. I also checked for weight limitations before buying it from the guy; this is what the website says:

Max rider weight of 300lbs:

All other bikes, including hybrids, urban, commuter, fitness, Ride+ electric assist, cyclocross, and all mountain bikes.

Things are sort of different here, most warranties will be honored for one or two years regardless of the stated duration (you will be blamed for any problems that occur after that period), dealers are not very commited to the brand; trek dealers here always deal other brands and most definitely will not honor the warranty if i'm not the original owner, which i'm not. So, that's pretty much out of the question.

Quite frankly i don't think i'll ever be riding this frame with confidence again; failure might not result in catastrophe, but i'd rather not risk it; i think i'll take the advice from FBinNY, davidad and aramis and just move all my components to a new frame that fits my height better so the weight doesn't cause so much stress on the seatpost (AND SHED SOME POUNDS! do I hear you say? hehe)

A small voice is telling me that a drop bar conversion on an aluminum hybrid designed for hybrid bars might have resulted in you doing more pulling on the bars, thereby putting more stress on the seat tube above the top tube, especially if you hammer a lot and go up a lot of steep hills. If there wasn't enough seatpost in the seat tube as others have stated, this might be a contributing factor.

I don't know if there's ever a way of knowing where there were microcracks in the seat tube to begin with or whether drop bar + hammering caused this. Either way, I wish you the best of luck with your frame.